As is already addressed in the previous answers, Mercerism is the dominant religion, in Philip K. Dick's novel, following World War Terminus, whose central tenets encourage empathy between humans in a world where that empathy—and the understanding of what it means to be human—is being eroded. The figure Dick chooses to represent the "Christ" persona in the religion is deliberately in the same mold as most savior archetypes. Mercer is an ordinary person who has suffered for no real reason, and for whom his followers can feel empathy because they know he doesn't deserve to be discriminated against.

It is true that, ultimately, "Mercerism" is exposed as a "scam," something created in a television studio with the goal of uniting people in empathy and communal feeling. However, the fact remains that regardless of the truths behind it, the religion generates the intended feelings in its followers, and it is very real to them. One of the questions Dick poses in the novel, then, is: what makes a religion "real"? Does it really matter whether the stories told within a religion are completely accurate and reflect reality, or are the positive effects of a religion sufficient to justify its existence? Dick's story suggests that it is only the small-minded who seek to tear down something whose effects are real, purely because it isn't strictly "true."

Mercerism is the religion created by Wilbur Mercer in Philip K. Dick's novel Do Androids Dream of Electric Sheep? Mercer is a cult figure who walks up a mountain while stones are thrown at him, resulting in his followers feeling the pain he feels (which "hurts like hell") as he is being stoned. This act of collective consciousness is made possible through the use of "Empathy Boxes" which connect the followers with Mercer's mind; although the followers may feel pain this way, they may also feel and spread joy.

Empathy Boxes support the  two major tenants of Mercerism: empathy for the individual and work for the good of the community. In that sense, followers of Mercerism believe that empathy leads to community, and community leads to empathy. 

Ultimately, as positive as this all sounds, Mercer is revealed to be a fraud— an actor named Al Jerry whose world was created on a soundstage.

Mercerism is a religion that spread on earth and the space colonies after World War Terminus whose main purpose is to unite humanity. This religion is founded upon the life and teachings of a man called Wilbur Mercer and is based on two principles: empathy to other individuals and working for the good of the community. The adherents of Mercerism use mood organs known as empathy boxes to enter into a world where everybody is connected to the rest of humanity. There is such a deep connection that when the followers view images of Mercer being stoned, they feel the exact physical pain he did. Even though Mercerism is exposed as a scam, and Mercer seconds the allegations as true, people do not abandon the religion. They choose to stay on because unlike the artificial world, Mercerism though not real kept human emotions alive by connecting humanity through empathy.

Mercerism is the fictional dominant religion depicted in Philip Dick's novel Do Androids Dream of Electric Sheep?

This religion was brought about by the religious cult figure, Wilbur Mercer. Mercer is required to walk endlessly up a mountain while stones are thrown down at him. His followers feel the same physical pain that he does as the rocks strike him repeatedly.

The religion is used to create the sense of a collective among its followers based upon the fact that they share the physical pains of their "leader." The followers of Mercer are linked together through "Empathy Boxes" which allow them to share in his pain.

The religion comes about after the "World War Terminus" which has destroyed the majority of the earth.